Boiler

ABSTRACT

An amount of scale adhering onto inner surfaces of water tubes in any one of various boilers including a steam boiler, a hot water boiler, a waste heat boiler, and an exhaust gas boiler is accurately known by providing a temperature sensor at an appropriate position of the boiler. A plurality of water tubes ( 5, 6 ) connecting between an upper header ( 3 ) and a lower header ( 4 ) constitute an inner water tube row ( 7 ) and an outer water tube row ( 8 ). Inner longitudinal fins ( 9 ) close gaps between the adjacent inner water tubes ( 5, 5 ) except at a lower end of the inner water tube row ( 7 ). Outer longitudinal fins ( 11 ) close gaps between the adjacent outer water tubes ( 6, 6 ) except at an upper end of the outer water tube row ( 8 ). A plurality of upper outer lateral fins ( 17 ) are provided in a vertical direction on a surface constituting an inner peripheral surface of the outer water tube row ( 8 ) in a predetermined region extending upward from an intermediate portion in the vertical direction of each of the outer water tubes ( 6 ). A temperature sensor ( 29 ) is provided to one of the outer water tubes ( 6 ) at a position corresponding to a lower end of the predetermined region. An adhesion state of the scale is known based on a temperature detected by the temperature sensor ( 29 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to various boilers including a steam boiler, a hot water boiler, a waste heat boiler, and an exhaust gas boiler.

The subject application claims a benefit of the priority of Japanese Patent Application No. 2007-261598 filed on Oct. 5, 2007, and contents thereof are herein incorporated.

2. Description of the Related Art

There are known as multitubular boilers ones disclosed in Japanese Patent Application Laid-open No. Hei 2-75805 (FIGS. 2 and 3). A boiler body of the boiler of this type includes a large number of water tubes arranged in a concentric cylindrical shape between an upper header and a lower header each formed in an annular shape. In such boiler body, an inside of an inner water tube row is a combustion chamber and an outside of the inner water tube row is a combustion gas flow path.

In this context, when a fuel is burned such that flame is generated from a burner installed in the upper portion of the boiler body toward the inside of the combustion chamber, a combustion gas is reversed in a lower portion of the combustion chamber and passes between the inner water tube row and the outer water tube row to be discharged as an exhaust gas to a flue from the upper portion of the boiler body. In the meantime, the combustion gas undergoes heat exchange with water in each of the water tubes, thereby heating the water in each of the water tubes.

In such boiler, when checking an adhesion state of scale in the water tubes is required, temperatures of the water tubes are Measured as disclosed in Japanese Patent Application Laid-open No. Hei 11-201406 (Paragraphs [0003] and [0009], and FIG. 1).

However, a position, at which a temperature sensor for monitoring an adhesion amount of scale is attached in the boiler, is not conventionally established. In the invention disclosed in Japanese Patent Application Laid-open No. Hei 11-201406, an attachment position for the temperature sensor is determined considering distinguishing adhesion of scale and adhesion of soot from each other. Therefore, the temperature sensor for monitoring the adhesion amount of scale is not provided at an optimum position considering a boiling state of water in each of water tubes, heat load in each of the water tubes, a relation with lateral fins provided to each of the water tubes, etc.

SUMMARY OF THE INVENTION

An object to be achieved by the present invention is therefore to accurately know an amount of scale adhering onto inner surfaces of the water tubes by providing a temperature sensor considering a boiling state of water in each of water tubes, heat load in each of the water tubes, a relation with lateral fins provided to each of the water tubes, etc.

The present invention has been made to achieve the above-mentioned object. According to a first aspect of the present invention, a boiler includes: a plurality of water tubes connecting between an upper header and a lower header; and a temperature sensor provided to one of a water-boiling start portion and a high-heat load portion of at least one of the plurality of water tubes.

According to the first aspect of the present invention, the temperature sensor is provided to one of the water-boiling start portion and the high-heat load portion of at least one of the plurality of water tubes. As the result of research, the inventor of the present invention found out that water is likely to be concentrated at the water-boiling start portion and the high-heat load portion and hence scale is likely to be precipitated to adhere to the water tubes. Therefore, it is possible to accurately know the amount of scale adhering onto the inner surfaces of the water tubes by measuring temperatures of the water-boiling start portion and the high-heat load portion.

According to a second aspect of the present invention, in the boiler according to the first aspect of the present invention, the plurality of water tubes are arranged to form a concentric cylindrical shape to constitute an inner water tube row and an outer water tube row. An inside of the inner water tube row serves as one of a combustion chamber and a space into which an exhaust gas is introduced, and a gas flow path is defined so as to deliver one of a combustion gas and the exhaust gas from the inside of the inner water tube row to an outside of the outer water tube row through between the inner water tube row and the outer water tube row. At least one of the inner water tube row and the outer water tube row is provided with lateral fins (at least one of upper inner lateral fins and upper outer lateral fins) only in a region extending from an intermediate portion of the gas flow path to a downstream portion thereof, or the lateral fins (at least one of upper inner lateral fins and upper outer lateral fins) located in the region extending from the intermediate portion of the gas flow path to the downstream portion thereof are provided to have an extending length extending from the plurality of water tubes larger than a length of a lateral fin (at least one of lower inner lateral fin and lower outer lateral fin) located upstream of the intermediate portion of the gas flow path. In the gas flow path, the temperature sensor is provided to the at least one of the plurality of water tubes at one of a position, at which one of the lateral fins located endmost among the lateral fins is provided, and a position, at which the extending length of the lateral fins is larger than the length of the lateral fin located upstream of the intermediate portion of the gas flow path.

A heat-receiving amount extremely increases at the position, at which one of the lateral fins located endmost among the lateral fins is provided, and at the position, at which the extending length of the lateral fins is larger the length of the lateral fin located upstream of the intermediate portion of the gas flow path, and hence water is likely to be concentrated at the above-mentioned positions so that scale is likely to be precipitated to adhere to the water tubes. Therefore, according to the second aspect of the present invention, it is possible to accurately know the amount of scale adhering onto the inner surfaces of the water tubes by providing the temperature sensor at one of the above-mentioned positions.

According to a third aspect of the present invention, in the boiler according to the second aspect of the present invention, of part of the plurality of water tubes constituting the outer water tube row, one of the part of the plurality of water tubes having a large heat-receiving amount is provided with the temperature sensor.

According to the third aspect of the present invention, of the part of the plurality of water tubes, one of the part of the plurality of water tubes having the large heat-receiving amount is provided with the temperature sensor. By providing the temperature sensor to the high-heat load portion of the high-heat load water tube to measure a temperature of the high-heat load portion, it is possible to more reliably and promptly know the amount of scale adhering onto the inner surfaces of the water tubes. In addition, the temperature sensor is provided to one of the part of the plurality of water tubes, and hence installation and maintenance of the temperature sensor are simplified.

According to a fourth aspect of the present invention, a boiler includes: a plurality of inner water tubes arranged to form a cylindrical shape between an upper header and a lower header to constitute an inner water tube row; a plurality of outer water tubes arranged to form a cylindrical shape between the upper header and the lower header so as to surround the inner water tube row to constitute an outer water tube row; a plurality of inner longitudinal fins provided to close gaps between the adjacent plurality of inner water tubes except at a lower end of the inner water tube row; a plurality of outer longitudinal fins provided to close gaps between the adjacent plurality of outer water tubes except at an upper end of the outer water tube row; outer lateral fins (upper outer lateral fins) provided on a surface constituting an inner peripheral surface of the outer water tube row in a predetermined region extending upward from an intermediate portion in a vertical direction of each of the plurality of outer water tubes; and a temperature sensor provided to one of a group including one of the plurality of outer water tubes, one of the plurality of outer longitudinal fins, and one of the outer lateral fins at a position corresponding to a lower end of the predetermined region.

The heat-receiving amount extremely increases at the position at which one of the outer lateral fins (upper outer lateral fins) located endmost among the outer lateral fins is provided, and hence water is likely to be concentrated at the above-mentioned position so that scale is likely to be precipitated to adhere to the water tubes. Therefore, according to the fourth aspect of the present invention, it is possible to accurately know the amount of scale adhering onto the inner surfaces of the water tubes by providing the temperature sensor at the above-mentioned position.

According to a fifth aspect of the present invention, a boiler includes: a plurality of inner water tubes arranged to form a cylindrical shape between an upper header and a lower header to constitute an inner water tube row; a plurality of outer water tubes arranged to form a cylindrical shape between the upper header and the lower header so as to surround the inner water tube row to constitute an outer water tube row; a plurality of inner longitudinal fins provided to close gaps between the adjacent plurality of inner water tubes except in one portion in a peripheral direction of the inner water tube row; a plurality of outer longitudinal fins provided to close gaps between the adjacent plurality of outer water tubes except in another portion in the peripheral direction of the outer water tube row; outer lateral fins provided on a surface constituting an inner peripheral surface of the outer water tube row in a predetermined region extending from an intermediate portion in the peripheral direction to the another portion in the peripheral direction of the outer water tube row; and a temperature sensor provided to one of a group including one of the plurality of outer water tubes, one of the plurality of outer longitudinal fins, and one of the outer lateral fins at a position corresponding to a side of one portion in the peripheral direction of the outer water tube row in the predetermined region.

The heat-receiving amount extremely increases at the position at which one of the lateral fins located endmost among the lateral fins is provided, and hence water is likely to be concentrated at the above-mentioned position so that scale is likely to be precipitated to adhere to the water tubes. Therefore, according to the fifth aspect of the present invention, it is possible to accurately know the amount of scale adhering onto the inner surfaces of the water tubes by providing the temperature sensor at the above-mentioned position.

In addition, according to a sixth aspect of the present invention, in the boiler according to the fifth aspect of the present invention, the temperature sensor is provided at a height corresponding to a height of a water-boiling start portion in one of the plurality of outer water tubes provided with the temperature sensor.

Water is likely to be concentrated at the water-boiling start portion in each of the water tubes, and hence scale is likely to be precipitated to adhere to the water tubes. Therefore, according to the sixth aspect of the present invention, by providing the temperature sensor at a position, at which one of the lateral fins located endmost among the lateral fins is provided in the peripheral direction, and a position close to the water-boiling start portion in a vertical direction, it is possible to further accurately know the amount of scale adhering onto the inner surfaces of the water tubes.

According to the boiler of the present invention, by providing the temperature sensor considering a boiling state of water in each of the water tubes, heat load in each of the water tubes, a relation with the lateral fins provided to each of the water tubes, etc., it is possible to accurately know the amount of scale adhering onto the inner surfaces of the water tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic longitudinal sectional view illustrating a boiler according to Example 1 of the present invention;

FIG. 2 is a sectional view taken along the line II-II of FIG. 1;

FIG. 3 is a partially enlarged sectional view taken along the line of FIG. 1;

FIG. 4 is a partially enlarged sectional view taken along the line IV-IV of FIG. 1; and

FIG. 5 is a schematic lateral sectional view illustrating a boiler according to Example 2 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Next, an embodiment of the present invention is described.

A boiler according to the present invention is not limited to a certain type, and is, for example, a steam boiler, a hot water boiler, a waste heat boiler, or an exhaust gas boiler. In any case, the boiler is a multitubular boiler and is typically a multitubular once-through boiler.

The boiler includes an upper header, a lower header, and a boiler body including a plurality of water tubes connecting between the upper header and the lower header. The upper header and the lower header are arranged at a vertical distance in parallel to each other, and the upper header and the lower header generally form a hollow annular shape. All the plurality of the water tubes are vertically arranged and connect between the upper header and the lower header. That is, each of upper ends of the water tubes are connected to the upper header, and each of lower ends thereof are connected to the lower header.

The water tubes are normally arranged between the upper header and the lower header in a peripheral direction thereof, thereby constituting a water tube row of a cylindrical shape. In this case, the water tube row is configured by two rows including an inner water tube row and an outer water tube row arranged in concentric cylindrical shapes. Note that, besides the inner water tube row and the outer water tube row, another water tubes or water tube row may be provided according to circumstances. Water tubes constituting the inner water tube row are referred to as inner water tubes, and water tubes constituting the outer water tube row are referred to as outer water tubes. As the boiler body including the inner water tube row and the outer water tube row, a following-flow boiler body and an ω (omega) flow boiler body described below can be exemplified.

First, in a case of the following-flow boiler body, in the inner water tubes arranged in a cylindrical shape, gaps between the adjacent inner water tubes are closed by inner longitudinal fins except at the lower end of the inner water tube row. With this configuration, the inner longitudinal fins are not provided at the lower end of the inner water tube row, and hence the gaps remain between the inner water tubes. The gaps are referred to as inner row communication portions. Meanwhile, in the outer water tubes arranged in a cylindrical shape, gaps between the adjacent outer water tubes are closed by outer longitudinal fins except at the upper end of the outer water tube row. With this configuration, the outer longitudinal fins are not provided at the upper end of the outer water tube row, and hence the gaps remain between the outer water tubes. The gaps are referred to as outer row communication portions.

In order to increase a heat transfer area, in the following-flow boiler body having the above-mentioned configuration, on an outer peripheral surface of the inner water tube row and/or an inner peripheral surface of the outer water tube row, lateral fins or the like extending outwardly from each of the water tubes may be provided. For example, in a predetermined region in a vertical direction of each of the inner water tubes, on a surface constituting the outer peripheral surface of the inner water tube row, a plurality of inner lateral fins may be provided at a vertical distance. Further, in a predetermined region in the vertical direction of each of the outer water tubes, on a surface constituting the inner peripheral surface of the outer water tube row, a plurality of outer lateral fins can be provided at a vertical distance.

Meanwhile, in a case of the ω flow boiler body, in the inner water tubes arranged in a cylindrical shape, gaps between the adjacent inner water tubes are closed by inner longitudinal fins except in one portion in the peripheral direction of the inner water tube row. With this configuration, the inner longitudinal fins are not provided in the one portion in the peripheral direction of the inner water tube row, and hence a gap is formed between the inner water tubes. The gap is referred to as an inner row communication portion. When the inner water tubes are arranged at equal intervals in the peripheral direction to constitute the inner water tube row, in the one portion in the peripheral direction of the inner water tube row, the inner row communication portion may be formed instead of providing one or a plurality of inner water tubes. Meanwhile, in the outer water tubes arranged in a cylindrical shape, gaps between the adjacent outer water tubes are closed by outer longitudinal fins except in the other portion in the peripheral direction of the outer water tube row (portion substantially opposed to the one portion in the peripheral direction of the inner water tube row). With this configuration, the outer longitudinal fins are not provided in the other portion in the peripheral direction of the outer water tube row, and hence a gap is formed between the outer water tubes. The gap is referred to as an outer row communication portion. When the outer water tubes are arranged at equal intervals in the peripheral direction to constitute the outer water tube row, in the other portion in the peripheral direction of the outer water tube row, the outer row communication portion may be formed instead of providing one or a plurality of outer water tubes.

In order to increase a heat transfer area, in the ω flow boiler body having the above-mentioned configuration, on an outer peripheral surface of the inner water tube row and/or an inner peripheral surface of the outer water tube row, lateral fins or the like extending outwardly from each of the water tubes may be provided. For example, in a predetermined region extending from an intermediate portion in the peripheral direction of the inner water tube row (intermediate portion between the one portion in the peripheral direction and the other portion in the peripheral direction of the inner water tube row) to the other portion in the peripheral direction of the inner water tube row, on a surface constituting the outer peripheral surface of the inner water tube row, a plurality of inner lateral fins may be provided to each of the inner water tubes at a vertical distance. Further, in a predetermined region extending from an intermediate portion in the peripheral direction of the outer water tube row to the other portion in the peripheral direction thereof, on a surface constituting the inner peripheral surface of the outer water tube row, a plurality of outer lateral fins can be provided to each of the outer water tubes at a vertical distance.

In both cases of the boiler body, the upper end of the boiler body is provided with a burner, and the lower end thereof is closed by a fireproof material. With this configuration, an inside of the inner water tube row constitutes a combustion chamber, and it is possible to burn a fuel so that flame is generated from the burner toward the combustion chamber. Note that, in a case of the waste heat boiler or the exhaust gas boiler, the boiler body is closed at one end thereof in the vertical direction and has an opening portion at the other end thereof in the vertical direction, through which an exhaust gas is introduced into the boiler body. That is, in this case, the inside of the inner water tube row serves as a space into which the exhaust gas is introduced.

Owing to such configuration, in the case of the following-flow boiler body, a combustion gas or the exhaust gas is introduced into a space between the inner water tube row and the outer water tube row through the inner row communication portions located at the lower end of the inner water tube row so as to be radially delivered from the outer row communication portions located at the upper end of the outer water tube row. Meanwhile, in the case of the ω flow boiler body, the combustion gas or the exhaust gas is introduced into the space between the inner water tube row and the outer water tube row through the inner row communication portion located in the one portion in the peripheral direction of the inner water tube row so as to be delivered from the other portion in the peripheral direction of the outer water tube row.

In both cases of the boiler body, an outer peripheral portion of the outer water tube row is provided with a boiler body cover of a cylindrical shape, and the exhaust gas is delivered to a flue through the boiler body cover. The boiler body cover may have any kinds of configuration as long as the boiler body cover receives the exhaust gas from the outer row communication portions of the outer water tube row to introduce the same to the flue. Typically, the boiler body cover is a cylindrical member provided between the upper header and the lower header so as to surround the outer water tube row. In this case, the upper end of the boiler body cover and the upper header are hermetically sealed. The lower end of the boiler body cover and the lower header are also hermetically sealed. A flue is connected to an upper portion of a peripheral side wall of the boiler body cover. In this case, the boiler body cover may have a configuration in which a swelling portion swelling outwardly in a radial direction is provided on part thereof and the exhaust gas is introduced to the flue through the swelling portion.

In order to monitor an adhesion state of scale (hard components precipitated out of water) adhering onto inner surfaces of the water tubes, a temperature sensor is attached to the boiler body. By monitoring temperatures of the water tubes with use of the temperature sensor, it is possible to know the adhesion state of scale. As the temperature sensor, a thermistor, etc. may be used and a thermocouple is suitably used.

As a result of research, the inventor of the present invention found out that, in a water-boiling start portion in each of the water tubes and a high-heat load portion of each of the water tubes, water is likely to be concentrated in the vicinity of water tube walls so that scale is likely to be precipitated to adhere to the water tubes. Therefore, for promptly knowing the adhesion state of scale, it is effective to provide the temperature sensor to the above-mentioned portions so as to monitor the adhesion state of scale based on temperatures of the portions. In this case, when heat load is different depending on the water tubes, it is preferred that the temperature sensor be provided to a water tube having a large heat-receiving amount. It is more preferred that, in the maximum heat load water tube having the largest heat-receiving amount, the temperature sensor be provided to the water-boiling start portion in the maximum heat load water tube or the maximum heat load portion of the maximum heat load water tube (portion having a heat-receiving amount which rapidly increases at a position at which an endmost heat transfer surface among heat transfer surfaces, such as lateral fins, is provided or at a position at which a length of the lateral fins extending from each of the water tubes is long).

In the following-flow boiler body, when lateral fins are provided in a predetermined region extending upward from the intermediate portion in the vertical direction of the inner water tube and/or the outer water tube, or when an extending length of the lateral fins is made long in the predetermined region, different heat load is applied to the water tube provided with the lateral fins in its axial direction. In this case, with respect to the water tube provided with the lateral fins, the temperature sensor is provided at a position corresponding to the water-boiling start portion in the water tube or the lower end of the predetermined region.

In the ω flow boiler body, when lateral fins are provided in a predetermined region extending from the intermediate portion in the peripheral direction of the inner water tube and/or the outer water tube to the other portion in the peripheral direction thereof, the water tubes are different from each other in heat load depending on existence of the lateral fins. In this case, within the predetermined region, at a position corresponding to a side of the one portion in the peripheral direction, the water tube provided with the endmost lateral fin is a maximum heat load water tube, and hence the temperature sensor is provided to the maximum heat load water tube. In this case, it is preferred that the temperature sensor be provided to the water-boiling start portion in the water tube provided with the temperature sensor.

In both cases, when, of the inner water tubes and the outer water tubes, one of the outer water tubes is provided with the temperature sensor, installation and maintenance of the temperature sensor are simplified. In this case, according to circumstances, the temperature sensor may be provided to one of the outer longitudinal fins or one of the outer lateral fins instead of one of the outer water tubes itself. Also in this case, the temperature sensor provided to one of the outer longitudinal fins or one of the outer lateral fins detects the temperature of the outer water tubes indirectly.

EXAMPLE 1

Hereinafter, specific examples according to the present invention are described in detail with reference to the drawings.

FIG. 1 is a schematic longitudinal sectional view illustrating a boiler according to Example 1 of the present invention. Further, FIG. 2 is a sectional view taken along the line II-II of FIG. 1. A boiler 1 according to this example is a multitubular once-through boiler including a boiler body 2 of a cylindrical shape. The boiler body 2 according to this example is configured as a so-called following-flow boiler body. Specifically, the boiler body 2 includes an upper header 3, a lower header 4, and a large number of water tubes 5 and 6 arranged to form a cylindrical shape to connect the upper header 3 to the lower header 4.

The upper header 3 and the lower header 4 are arranged at a vertical distance in parallel to each other. Each of the upper header 3 and the lower header 4 forms a hollow annular shape. Further, the upper header 3 and the lower header 4 are arranged horizontally and coaxially.

The water tubes 5 are vertically arranged. Upper ends of the water tubes 5 are connected to the upper header 3, and lower ends thereof are connected to the lower header 4. The water tubes 5 are successively arranged in the peripheral direction of the upper header 3 and the lower header 4, thereby constituting a water tube row of a cylindrical shape. Meanwhile, the water tubes 6 are also vertically arranged, the upper ends of the water tubes 6 are connected to the upper header 3, and the lower ends of the water tubes 6 are connected to the lower header 4. The water tubes 6 are successively arranged in the peripheral direction of the upper header 3 and the lower header 4, thereby constituting a water tube row of a cylindrical shape. In this example, an inner water tube row 7 and an outer water tube row 8 are arranged in concentric cylindrical shapes. The inner water tube row 7 includes the inner water tubes 5 arranged in a cylindrical shape. Meanwhile, the outer water tube row 8 includes the outer water tubes 6 arranged in a cylindrical shape so as to surround the inner water tube row 7.

The inner water tube row 7 is provided with, except in a predetermined region at a lower end thereof, inner longitudinal fins 9 such that gaps between the adjacent inner water tubes 5 and 5 are closed. That is, the gaps between the adjacent inner water tubes 5 and 5 are closed by the inner longitudinal fins 9 except in the predetermined region at the lower end thereof. At the lower end of the inner water tube row 7, at which the inner longitudinal fins 9 are not provided, the gaps remain between the adjacent inner water tubes 5 and 5. The gaps constitute inner row communication portions 10, and communication is established between an inside and an outside of the inner water tube row 7 through the inner row communication portions 10.

The outer water tube row 8 is provided with, except in a predetermined region at an upper end thereof, outer longitudinal fins 11 such that gaps between the adjacent outer water tubes 6 and 6 are closed. That is, the gaps between the outer water tubes 6 and 6 are closed by the outer longitudinal fins 11 except in the predetermined region at the upper end thereof. At the upper end of the outer water tube row 8, at which the outer longitudinal fins 11 are not provided, gaps remain between the adjacent outer water tubes 6 and 6. The gaps constitute outer row communication portions 12, and communication is established between an inside and an outside of the outer water tube row 8 through the outer row communication portions 12.

Incidentally, in the illustrated example, the lower end of each of the inner water tubes 5 is formed into a small diameter portion 13 having a diameter smaller than that of the portion above the lower end thereof. The small diameter portions 13 are provided so as to ensure a desired flow rate of the combustion gas passing through the inner row communication portions 10. Accordingly, in a case where the desired flow rate of the combustion gas passing through the inner row communication portions 10 can be ensured, the small diameter portions 13 may not be provided. A size of each of the inner row communication portions 10 depends on the gap between the adjacent inner water tubes 5 and 5 and a position of the lower end of the inner longitudinal fin 9 in a height direction thereof. Accordingly, instead of providing the small diameter portions 13, those dimensions may be adjusted. Meanwhile, in the illustrated example, the small diameter portion is not formed on the upper end of each of the outer water tubes 6. However, similarly to each of the inner water tubes 5, the small diameter portion may be formed thereon.

FIG. 3 is a partially enlarged sectional view taken along the line of FIG. 1. Further, FIG. 4 is a partially enlarged sectional view taken along the line IV-IV of FIG. 1. As illustrated in FIGS. 1 to 4, according to needs, each of the inner water tubes 5 may be further provided with an enlarged heat transfer surface protruding from the outer peripheral surface thereof. In the illustrated example, each of the inner water tubes 5 is provided with inner lateral fins 14 and 15 on a surface constituting the outer peripheral surface of the inner water tube row 7. In this case, the upper inner lateral fins 14 are provided in an upper region of each of the inner water tubes 5, and the lower inner lateral fins 15 are provided in a lower region thereof.

Specifically, in the upper half region of each of the inner water tubes 5, on the surface constituting the outer peripheral surface of the inner water tube row 7, the plurality of upper inner lateral fins 14 are provided to extend in a flange-like shape in a radially outward direction of each of the inner water tubes 5. In the illustrated example, a large number of upper inner lateral fins 14 are provided at equal vertical intervals. Further, as illustrated in FIG. 3, according to needs, cutouts 16 for relaxing thermal stress are formed in a distal end of each of the upper inner lateral fins 14. Meanwhile, in the lower half region of each of the inner water tubes 5 except in the small diameter portion 13, on the surface constituting the outer peripheral surface of the inner water tube row 7, the plurality of lower inner lateral fins 15 are provided to extend in a flange-like shape in the radially outward direction of each of the inner water tubes 5. In the illustrated example, a large number of lower inner lateral fins 15 are provided at equal vertical intervals. Similarly to each of the upper inner lateral fins 14, according to needs, a cutout (not shown) for relaxing the thermal stress may be formed in a distal end of each of the lower inner lateral fins 15. The upper inner lateral fins 14 and the lower inner lateral fins 15 are not particularly limited in length extending from the outer peripheral surface of each of the inner water tubes 5. However, in order to prevent the lower inner lateral fins 15 from being overheated, it is preferred that the lower inner lateral fins 15 be formed to have a length extending from the outer peripheral surface of each of the inner water tubes 5 smaller than that of the upper inner lateral fins 14. Though the lower inner lateral fins 15 are typically formed to have a length larger than a half length of the upper inner lateral fins 14, the lower inner lateral fins 15 are formed to have a length smaller than an entire length of the upper inner lateral fins 14.

Further, similarly, according to needs, each of the outer water tubes 6 may be further provided with an enlarged heat transfer surface protruding from the outer peripheral surface thereof. In the illustrated example, each of the outer water tubes 6 is provided with outer lateral fins 17 and 18 on a surface constituting the inner peripheral surface of the outer water tube row 8. In this case, the upper outer lateral fins 17 are provided in an upper region of each of the outer water tubes 6, and the lower outer lateral fins 18 are provided in a lower region thereof.

Specifically, in the upper half region of each of the outer water tubes 6, on the surface constituting the inner peripheral surface of the outer water tube row 8, the plurality of upper outer lateral fins 17 are provided to extend in a flange-like shape in a radially outward direction of each of the outer water tubes 6. In the illustrated example, a large number of upper outer lateral fins 17 are provided at equal vertical intervals. Further, as illustrated in FIG. 3, according to needs, cutouts 19 for relaxing the thermal stress are formed in a distal end of each of the upper outer lateral fins 17. Meanwhile, in the lower half region of each of the outer water tubes 6, on the surface constituting the inner peripheral surface of the outer water tube row 8, the plurality of lower outer lateral fins 18 are provided to extend in a flange-like shape in the radially outward direction of each of the outer water tubes 6. In the illustrated example, a large number of lower outer lateral fins 18 are provided at equal vertical intervals. Similarly to each of the upper outer lateral fins 17, according to needs, a cutout (not shown) for relaxing the thermal stress may be formed in a distal end of each of the lower outer lateral fins 18. The upper outer lateral fins 17 and the lower outer lateral fins 18 are not particularly limited in length extending from the outer peripheral surface of each of the outer water tubes 6. However, in order to prevent the lower outer lateral fins 18 from being overheated, it is preferred that the lower outer lateral fins 18 be formed to have a length extending from the outer peripheral surface of each of the outer water tubes 6 smaller than that of the upper outer lateral fins 17. Though the lower outer lateral fins 18 are typically formed to have a length larger than a half length of the upper outer lateral fins 17, the lower outer lateral fins 18 are formed to have a length smaller than an entire length of the upper outer lateral fins 17.

Incidentally, the inner water tubes 5 are arranged alternately with the outer water tubes 6 along the peripheral direction of the boiler body 2. Further, the inner lateral fins 14 and 15 and the outer lateral fins 17 and 18 are adjusted in size, shape, and arrangement thereof such that, in a plan view of the boiler body 2, the inner lateral fins 14 and the outer lateral fins 17 do not overlap each other and the inner lateral fins 15 and the outer lateral fins 18 do not overlap each other. Further, the upper inner lateral fins 14 and the upper outer lateral fins 17, and the lower inner lateral fins 15 and the lower outer lateral fins 18 may all be installed horizontally, and may be provided to be inclined upward along the one-way peripheral direction of the boiler body 2. In this example, the inner lateral fins 14 and 15 and the outer lateral fins 17 and 18 are provided to be inclined at the same predetermined angle with respect to an axial direction (perpendicular direction) of each of the water tubes 5 and 6. Such inclination angle is set to, for example, 80 degrees. With this configuration, in a case where the lateral fins 14, 15, 17, and 18 are inclined with respect to a horizontal direction, by agitating the combustion gas flowing upward in a combustion gas flow path 27 formed between the inner water tube row 7 and the outer water tube row 8, it is possible to enhance performance in heat transfer from the combustion gas to the water tubes 5 and 6. Note that, presence/absence of installation of each of the lateral fins 14, 15, 17 and 18, an installation region and an installation position thereof, the number of lateral fins to be installed, a shape, a size, and the like can be modified as appropriate.

Further, between the upper header 3 and the lower header 4, a boiler body cover 20 of a cylindrical shape is provided so as to surround the outer water tube row 8. An upper end of the boiler body cover 20 and the upper header 3 are hermetically sealed. A lower end of the boiler body cover 20 and the lower header 4 are also hermetically sealed. A flue 21 is connected to an upper portion of a peripheral side wall of the boiler body cover 20 at a desired position in the peripheral direction thereof. In the illustrated example, a large diameter portion 22 is formed on the upper end of the boiler body cover 20, and the flue 21 is connected to the peripheral side wall of the large diameter portion 22.

A lower surface of the upper header 3 is provided with a fireproof material 23 covering connection portions between the upper header 3 and the inner water tubes 5 and connection portions between the upper header 3 and the outer water tubes 6. An upper surface of the lower header 4 is also provided with another fireproof material 23 covering connection portions between the lower header 4 and the inner water tubes 5 and connection portions between the lower header 4 and the outer water tubes 6. In this case, the fireproof material 23 on the lower header 4 side is provided so as to also close a central portion of the lower header 4. A central portion of the fireproof material 23 on the lower header 4 side has a recess 24 of a columnar shape or a truncated cone shape formed therein.

In a central portion of the upper header 3, there is provided a burner 25 for generating flame downward. The burner 25 is supplied with a fuel and a combustion air. By operating the burner 25, combustion of the fuel is performed in the boiler body 2. In this case, an inside of the inner water tube row 7 functions as a combustion chamber 26.

The combustion gas generated by the combustion of the fuel in the combustion chamber 26 is delivered to the combustion gas flow path 27 between the inner water tube row 7 and the outer water tube row 8 through the inner row communication portions 10. Further, the combustion gas is radially delivered from the upper portion of the outer water tube row 8 through the outer row communication portions 12 to be received in the boiler body cover 20. The combustion gas is then discharged as an exhaust gas to the outside through the flue 21 connected to the boiler body cover 20. In the meantime, the combustion gas undergoes heat exchange with water in the water tubes 5 and 6. As a result, the water in the water tubes 5 and 6 is heated. In this manner, the heated water can be taken out from the upper header 3 in a form of steam. The taken-out steam is sent to steam-using-equipment (not shown) through a water separator (not shown) or the like.

Between the outer water tube row 8 and the boiler body cover 20, a space is defined to have a cylindrical form. The space is charged with a heat insulating material 28 in a region extending to a predetermined height from the upper surface of the fireproof material 23 on the lower header 4 side. The heat insulating material 28 may be of any type such as one made of ceramic fibers or rock wool. In the illustrated example, the heat insulating material 28 is charged in the space between the outer water tube row 8 in a region lower than the outer row communication portions 12 and the boiler body cover 20 in a region lower than the large diameter portion 22.

A temperature sensor 29 using a thermocouple or the like is provided to any one of the water tubes 5 and 6 of the boiler 1. The temperature sensor 29 is provided so as to monitor an adhesion state of scale adhering onto inner surfaces of the water tubes 5 and 6 by detecting a temperature at a position at which the temperature sensor 29 is provided. In this example, the temperature sensor 29 is provided to one of the outer water tubes 6, and is provided at a lower end in a region in which the upper outer lateral fins 17 are provided. That is, of the plurality of upper outer lateral fins 17 provided vertically, on the lower portion of the upper outer lateral fin 17 arranged on the lowest position, the temperature sensor 29 is provided. The lowest position corresponds to a gap between the lower end in the region in which the upper outer lateral fins 17 are provided, and an upper end in a region in which the lower outer lateral fins 18 are provided.

The temperature sensor 29 may be provided to any one of the outer water tubes 6. However, in the illustrated example, the temperature sensor 29 is provided to the outer water tube 6 located substantially opposed to the flue 21. Further, any method may be adopted to attach the temperature sensor 29 to the outer water tube 6. As illustrated in FIG. 3, an attaching seat 30 is fixed by welding to the outer water tube 6 along the peripheral direction of the outer water tube 6, and the temperature sensor 29 is inserted into the attaching seat 30. As a result, attachment is easily performed. In this case, the attaching seat 30 passes through one of the outer longitudinal fins 11 from the outside of the outer water tube row 8, and is provided to extend to the inside of the outer water tube row 8. In this case, it is preferred that a distal end of the attaching seat 30 extend to a position corresponding to a central portion in a width direction of one of the upper outer lateral fins 17 to be fixed onto the outer peripheral surface of the outer water tube 6.

The attaching seat 30 has an attachment hole (not shown) formed therein along an extending direction of the attaching seat 30. The attachment hole is opened toward a proximal end of the attaching seat 30 but does not extend to the distal end of the attaching seat 30. Therefore, only by inserting the temperature sensor 29 up to the bottom of the attachment hole from the outside of the outer water tube row 8, it is possible to install the temperature sensor 29 in the inside of the outer water tube row 8. Incidentally, the attachment hole may be formed into a groove-like shape to be opened toward the inner peripheral surface of the attaching seat 30 curved in an arc shape. In this case, the attaching seat 30 is installed on the outer water tube 6 so that a bottomed hole is formed between the outer peripheral surface of the outer water tube 6 and the attaching seat 30.

The temperature sensor 29 is provided to the outer water tube 6 to detect a temperature of the outer water tube 6. However, according to circumstances, the temperature sensor 29 may be provided to the outer longitudinal fin 11 or the upper outer lateral fin 17 to indirectly detect the temperature of the outer water tube 6 based on a temperature of the outer longitudinal fin 11 or the upper outer lateral fin 17. Further, in this example, the temperature sensor 29 is provided on the lower portion of the upper outer lateral fin 17 located lowest, and such provision means that the temperature sensor 29 is provided on a high-heat load portion of the outer water tube 6. Note that, instead of or in addition to the high-heat load portion, the temperature sensor 29 may be provided at a position corresponding to a water-boiling start portion in the outer water tube 6.

Specifically, the water-boiling start portion in each of the outer water tubes 6 is located at a distance above the upper surface of the fireproof material 23 on the lower header 4 side by one-tenth of a separation distance L between the lower surface of the fireproof material 23 on the upper header 3 side and the upper surface of the fireproof material 23 on the lower header 4 side.

During operation of the boiler 1, the temperature sensor 29 monitors the adhesion state of scale based on the temperature of the outer water tube 6. If a detection temperature of the temperature sensor 29 exceeds a set temperature, the temperature sensor 29 may output information that more than a predetermined amount of scale adheres. To deal with such problem, it is preferred that, after discharging water in the boiler body 2, a removing work for the scale be performed with chemicals.

According to the configuration in this example, the temperature sensor 29 is provided on the high-heat load portion of the water tube 5 or 6 and/or the water-boiling start portion in the water tube 5 or 6. By monitoring the temperatures of the portions in which water in the water tubes 5 and 6 is likely to be concentrated so that scale is likely to be precipitated to adhere to the water tubes, it is possible to know the adhesion state of scale in the water tubes 5 and 6 promptly and accurately. Soft water is normally used in the boiler 1 to prevent adhesion of scale. In this context, according to the configuration in this example, it is possible to promptly deal with hardness leak, etc. due to a failure of a water softener.

EXAMPLE 2

FIG. 5 is a schematic lateral sectional view illustrating a boiler according to Example 2 of the present invention. The boiler according to Example 2 is basically the same as the boiler 1 according to Example 1. Hereinafter, description is centered on a difference therebetween, and description of similarity is omitted. Further, corresponding portions are denoted by the same reference symbols.

The boiler 1 according to Example 1 includes the following-flow boiler body having a configuration as described below. In the configuration, the combustion gas from the burner 25 is introduced into the combustion gas flow path 27 formed between the inner water tube row 7 and the outer water tube row 8 through the inner row communication portion 10 at the lower end of the inner water tube row 7, and the combustion gas is delivered radially from the outer row communication portion 12 at the upper end of the outer water tube row 8. The boiler 1 according to Example 2 includes thew flow boiler body having a configuration as described below. In the configuration, the combustion gas from the burner 25 is introduced into the combustion gas flow path 27 formed between the inner water tube row 7 and the outer water tube row 8 through the inner row communication portion 10 provided on the one portion in the peripheral direction of the inner water tube row 7 (on the right side in FIG. 5), and the combustion gas is delivered to the outside of the outer water tube row 8 through the outer row communication portion 12 provided on the other portion in the peripheral direction of the outer water tube row 8 (on the left side in FIG. 5). The reason why the boiler body according to Example 2 is called the ω flow boiler body is that the combustion gas flows in a laterally-oriented ω shape as described above.

In Example 1, the gaps between the adjacent inner water tubes 5 and 5 are closed by the inner longitudinal fins 9 except in the predetermined regions at the lower ends of the inner water tubes 5. Meanwhile, in Example 2, the gaps between the adjacent inner water tubes 5 and 5 are closed by the inner longitudinal fins 9 in entire regions in the vertical direction of the gaps except at a right end in FIG. 5. At the right end in FIG. 5, no inner longitudinal fin 9 is provided to the gaps between the adjacent inner water tubes 5 and 5, and a gap is formed in an entire region in the vertical direction to constitute the inner row communication portion 10. When the inner row communication portion 10 is formed, of the inner water tubes 5 arranged at equal intervals in the peripheral direction, at the right end in FIG. 5, installation of one or a plurality of inner water tubes 5 may be omitted.

In Example 1, the gaps between the adjacent outer water tubes 6 and 6 are closed by the outer longitudinal fins 11 except in the predetermined regions at the upper ends of the outer water tubes 6. Meanwhile, in Example 2, the gaps between the adjacent outer water tubes 6 and 6 are closed by the outer longitudinal fins 11 in entire regions in the vertical direction of the gaps except at a left end in FIG. 5. At the left end in FIG. 5, no outer longitudinal fin 11 is provided to the gaps between the adjacent outer water tubes 6 and 6, and a gap is formed in an entire region in the vertical direction to constitutes the outer row communication portion 12. When the outer row communication portion 12 is formed, of the outer water tubes 6 arranged at equal intervals in the peripheral direction, at the left end in FIG. 5, installation of one or a plurality of outer water tubes 6 may be omitted.

In the case of Example 2, the combustion gas delivered outwardly from the combustion chamber 26 through the inner row communication portion 10 is diverged to opposite sides in the peripheral direction, and is then delivered outwardly from the outer row communication portion 12 through the combustion gas flow paths 27 and 27 on the opposite sides in the peripheral direction of the boiler body 2. In each of the combustion gas flow paths 27, in a predetermined region extending from an intermediate portion to a downstream portion thereof, the inner lateral fins 14 and/or the outer lateral fins 17 are provided. In this example, as illustrated in FIG. 5, of a region between the inner row communication portion 10 at the right end in FIG. 5 and the outer row communication portion 12 at left end in FIG. 5, in the region extending from the intermediate portion to the downstream portion of the combustion gas flow path 27, the inner lateral fins 14 and the outer lateral fins 17 are provided.

In this case, the plurality of inner lateral fins 14 are provided at equal vertical intervals on the surface constituting the outer peripheral surface of the inner water tube row 7 in the entire regions in the vertical direction of the inner water tubes 5 provided with the inner lateral fins 14, and extend in a flange-like shape in the radially outward direction of each of the inner water tubes 5. Further, the plurality of outer lateral fins 17 are provided at equal vertical intervals on the surface constituting the inner peripheral surface of the outer water tube row 8 in the entire regions in the vertical direction of the outer water tubes 6 provided with the outer lateral fins 17, and extend in a flange-like shape in the radially outward direction of each of the outer water tubes 6.

Also in Example 2, the inner water tubes 5 are arranged alternately with the outer water tubes 6 along the peripheral direction of the boiler body 2. Further, the inner lateral fins 14 and the outer lateral fins 17 are adjusted in size, shape, and arrangement thereof such that, in a plan view of the boiler body 2, the inner lateral fins 14 and the outer lateral fins 17 do not overlap each other. In Example 2, though the inner lateral fins 14 and the outer lateral fins 17 are installed horizontally, the inner lateral fins 14 and the outer lateral fins 17 may be inclined according to circumstances as in the case of Example 1.

Also in Example 2, though the boiler body cover 20 covers the outer water tube row 8 from the outside, the flue 21 is installed to the boiler body cover 20 on the left side thereof provided with the outer row communication portion 12. In this case, the flue 21 may be connected to the boiler body cover 20 at any position in the vertical direction of the boiler body 2. Further, similarly to Example 1, a large diameter portion may be provided on part of the boiler body cover 20. Alternatively, part of a left side wall of the boiler body cover 20 provided with the outer row communication portion 12 is swelled outwardly along the vertical direction, and thus the flue 21 may be connected to the swelled portion.

In the case of Example 2, in the predetermined region extending from the intermediate portion of the combustion gas flow path 27 to the outer row communication portion 12, the lateral fins 14 and 17 are provided on the inner water tubes 5 and the outer water tubes 6. Consequently, depending on presence/absence of the lateral fins 14 and 17, the water tubes are different from each other in heat load. In this case, the water tubes 5 and 6, which are provided with the endmost lateral fins 14 and 17 at the end on the upstream side in the predetermined region, serve as maximum heat load water tubes, and hence the temperature sensor 29 is provided to one of the maximum heat load water tubes (outer water tube 6 in the illustrated example). In this case, it is preferred that the temperature sensor 29 be provided on the water-boiling start portion in the water tube 6 provided with the temperature sensor 29. With this configuration, it is possible to promptly and accurately monitor the adhesion state of scale adhering in the water tubes 6.

The boiler 1 of the present invention is not limited to the above-mentioned examples and can be modified. In particular, as long as the boiler 1 has a configuration in which the temperature sensor 29 is provided to a water-boiling start portion of a water tube having a large heat-receiving amount (preferably, maximum heat load water tube) and/or a high-heat load portion (preferably, maximum heat load portion) of the water tube, a boiler body structure, such as the number of the water tubes 5 and 6 and arrangement thereof, can be modified as appropriate.

For example, in the following-flow boiler body according to Example 1, the inner water tubes 5 and/or the outer water tubes 6 may be bulge tubes in which recesses (small diameter portions) are formed alternately with protrusions (large diameter portions) in the vertical direction. In this case, the temperature sensor 29 may be provided at a lower end (at end position in a concavo-convex region) in a region in which the recesses and the protrusions are formed.

Further, in the ω flow boiler body according to Example 2, the outer water tubes 6 on the outer row communication portion 12 side may be provided with fins in entire peripheries thereof similarly to aerofin tubes. In this case, the outer water tubes 6 provided with the fins in the entire peripheries thereof are arranged on the inner side in the radial direction of the boiler body 2 with respect to the other outer water tubes 6. Further, in the w flow boiler body, some water tubes may be installed in the combustion chamber 26. In addition, according to circumstances, the boiler body 2 is not limited to the following-flow boiler body as in Example 1 and the ω flow boiler body as in Example 2, and may be another boiler body. It is needless to say that a water tube provided with the temperature sensor 29 for checking the adhesion state of scale and an attachment position of the temperature sensor 29 are different from those in the above-mentioned examples according to a change of the boiler body structure.

Further, in each of the above-mentioned examples, considering installation and maintenance of the temperature sensor 29, the temperature sensor 29 is provided to the outer water tube 6. However, instead of or in addition to such provision, the temperature sensor 29 may be provided to the inner water tube 5. Further, in each of the above-mentioned examples, instead of providing the burner 25, by providing a structure with which an exhaust gas is introduced into the inside of the inner water tube row 7, the boiler of the present invention may constitute a waste heat boiler or an exhaust gas boiler.

In addition, in Example 1, the lower inner lateral fins 15 and the lower outer lateral fins 18 may be pin-like studs protruding outwardly in the radial direction from the inner water tubes 5 or the outer water tubes 6. In this case, a plurality of studs are provided at equal intervals in the peripheral direction of the inner water tubes 5 or the outer water tubes 6, and a large number of studs are provided at equal intervals in the vertical direction thereof. Further, in Example 1, there may be adopted a configuration in which no lateral fin (lower inner lateral fins 15 and lower outer lateral fins 18) and no stud are provided in lower regions of the inner water tubes 5 and/or the outer water tubes 6.

In addition, in Example 1, installation regions for the lateral fins 14, 15, 17, and 18 are determined by partitioning the regions at the central portions in the vertical direction of the water tubes 5 and 6. However, the boundaries are not limited to the central portions in the vertical direction and can be modified as appropriate.

In the present invention, in various boilers including a steam boiler, a hot water boiler, a waste heat boiler, and an exhaust gas boiler, a temperature sensor is provided considering a boiling state of water in each of water tubes, heat load in each of the water tubes, a relation with lateral fins provided to each of the water tubes, etc. As a result, it is possible to accurately know an amount of scale adhering onto inner surfaces of the water tubes. 

1. A boiler, comprising: a plurality of water tubes connecting between an upper header and a lower header; and a temperature sensor provided to one of a water-boiling start portion and a high-heat load portion of at least one of the plurality of water tubes.
 2. A boiler according to claim 1, wherein: the plurality of water tubes are arranged to form a concentric cylindrical shape to constitute an inner water tube row and an outer water tube row; an inside of the inner water tube row serves as one of a combustion chamber and a space into which an exhaust gas is introduced; a gas flow path is defined so as to deliver one of a combustion gas and the exhaust gas from the inside of the inner water tube row to an outside of the outer water tube row through between the inner water tube row and the outer water tube row; at least one of the inner water tube row and the outer water tube row is provided with lateral fins only in a region extending from an intermediate portion of the gas flow path to a downstream portion thereof, or the lateral fins located in the region extending from the intermediate portion of the gas flow path to the downstream portion thereof are provided to have an extending length extending from the plurality of water tubes larger than a length of a lateral fin located upstream of the intermediate portion of the gas flow path; and in the gas flow path, the temperature sensor is provided to the at least one of the plurality of water tubes at one of a position, at which one of the lateral fins located endmost among the lateral fins is provided, and a position, at which the extending length of the lateral fins is larger than the length of the lateral fin located upstream of the intermediate portion of the gas flow path.
 3. A boiler according to claim 2, wherein, of part of the plurality of water tubes constituting the outer water tube row, one of the part of the plurality of water tubes having a large heat-receiving amount is provided with the temperature sensor.
 4. A boiler, comprising: a plurality of inner water tubes arranged to form a cylindrical shape between an upper header and a lower header to constitute an inner water tube row; a plurality of outer water tubes arranged to form a cylindrical shape between the upper header and the lower header so as to surround the inner water tube row to constitute an outer water tube row; a plurality of inner longitudinal fins provided to close gaps between the adjacent plurality of inner water tubes except at a lower end of the inner water tube row; a plurality of outer longitudinal fins provided to close gaps between the adjacent plurality of outer water tubes except at an upper end of the outer water tube row; outer lateral fins provided on a surface constituting an inner peripheral surface of the outer water tube row in a predetermined region extending upward from an intermediate portion in a vertical direction of each of the plurality of outer water tubes; and a temperature sensor provided to one of a group including one of the plurality of outer water tubes, one of the plurality of outer longitudinal fins, and one of the outer lateral fins at a position corresponding to a lower end of the predetermined region.
 5. A boiler, comprising: a plurality of inner water tubes arranged to form a cylindrical shape between an upper header and a lower header to constitute an inner water tube row; a plurality of outer water tubes arranged to form a cylindrical shape between the upper header and the lower header so as to surround the inner water tube row to constitute an outer water tube row; a plurality of inner longitudinal fins provided to close gaps between the adjacent plurality of inner water tubes except in one portion in a peripheral direction of the inner water tube row; a plurality of outer longitudinal fins provided to close gaps between the adjacent plurality of outer water tubes except in another portion in the peripheral direction of the outer water tube row; outer lateral fins provided on a surface constituting an inner peripheral surface of the outer water tube row in a predetermined region extending from an intermediate portion in the peripheral direction to the another portion in the peripheral direction of the outer water tube row; and a temperature sensor provided to one of a group including one of the plurality of outer water tubes, one of the plurality of outer longitudinal fins, and one of the outer lateral fins at a position corresponding to a side of one portion in the peripheral direction of the outer water tube row in the predetermined region.
 6. A boiler according to claim 5, wherein the temperature sensor is provided at a height corresponding to a height of a water-boiling start portion in one of the plurality of outer water tubes provided with the temperature sensor. 